The present invention relates to the process for the detoxification of effluents obtained in a variety of ore processing operations utilizing hydrogen peroxide and a magnetic pre-separation stage.
Purification of waste waters and recovery of components thereof is of major importance in connection with protection of the environment. Effluents from a variety of mining operations, particularly effluents from precious metal extraction plants and base metal flotation plants often contain cyanide in various forms together with toxic metals. The recovery of such substances and the removal thereof from effluent is of paramount importance before such waste waters are discharged in order to avoid serious damage to the environment and adverse impact on public health and safety.
A number of methods have been developed over the years of the treatment of such effluents. One of the best of the known methods for treating effluents originating from mining operations involves the oxidation of the cyanide contained in the waste water with hydrogen peroxide. Heavy metals contained in such waste effluents are usually removed by precipitation as a part of the overall process. These methods have been used successfully on a commercial scale for a number of years and are known to have a number of advantages over the even older methods such as treatment with chlorine because the excess hydrogen peroxide that is utilized decomposes to give ony water and oxygen. In the older methods involving chlorine, undesirable salts were formed and introduced into the waste water. The utilization of hydrogen peroxide overcomes the disadvantages associated with methods which involve salt formation and the introduction of those salts into waste water.
In many such operations, the waste effluent takes the form of so-called tailings pulp or slurry wherein the proportion of solids may be 50% or higher. Hydrogen peroxide has been successfully used to treat such pulp containing effluents and has been demonstrated on a commercial scale. In such operations, it has been found that the processing of some types of ore leads to tailings pulp which requires very large amounts of hydrogen peroxide for treatment. In such cases, the economic viability of the detoxification process depends on reducing the consumption of effluent treatment chemicals as far as possible.
One method for reducing the consumption of hydrogen peroxide by accurate measurement of the oxidizing agent demand and control of the dosage thereof is shown in U.S. Pat. No. 4,416,786, assigned to the same assignee as the present application and which is relied on and incorporated herein by reference. This method has been shown to be successful in preventing unnecessary excess dosing of the hydrogen peroxide. It is also been found to be suitable for adapting the dosage to change in concentrations of cyanide and other oxidizable substances in the effluent. It has been found, however, that if tailings contain solids which cause catalytic decomposition of the hydrogen peroxide, there could result a wastage of the reagent.
It is a purpose of the present invention therefore to prevent or minimize the unnecessary excess or waste of hydrogen peroxide during the treatment of effluent obtained from mining operations which may be caused by certain solid components of the tailings pulp.